Disruption of the anterior cruciate ligament (ACL) is a common injury that usually requires surgical reconstruction to restore function and prevent the progression of post- traumatic osteoarthritis (OA). However, evidence suggests that OA persists despite surgery. The initial tension applied to the graft at the time of surgery controls knee motion and the distribution of joint contact stress, factors thought to induce OA. Our primary objective is to evaluate the effects of initial graft tension on the articular cartilage response following ACL reconstruction in a prospective, randomized, double-blinded controlled study. Patients who were candidates for ACL reconstruction with an autograft were randomized into one of two treatment groups: 1) initial graft tension set such that the anterior-posterior (A-P) laxity of the reconstructed knee is equal to that of the contralateral normal knee (the low-tension treatment), and 2) initial graft tension set to reduce A-P laxity by 2-mm relative to that of the contralateral knee (the high-tension treatment). An additional group of subjects without evidence of knee injury was recruited to serve as a control. In the current funding cycle, the short-term outcome (<3 years) is being assessed. In this competitive renewal, the follow-up will be extended to a minimum of 7-years. The long-term follow-up is necessary to clearly identify those patients who will present with osteoarthritis. Joint space narrowing via radiography is the only validated measure for quantifying OA progression, and will continue to serve as the primary outcome measure for the study. Quantitative and semi-quantitative MRIs will also be used to assess cartilage volume loss and the integrity of related tissues. The effects of initial graft tension will also be assessed using the secondary outcome measures of A-P laxity (an indicator of graft integrity and knee kinematics), isokinetic strength (an indicator of dynamic function), and validated patient-oriented and clinical outcome scores. We hypothesize that after 7-years of healing, the tibiofemoral joint space width and cartilage thickness in the reconstructed knees of the high-tension treatment group will be equal to those of the control group, while that of the the low- tension treatment group will be less than those of the control group (indicating OA). We also expect that those patients with increased laxity following surgery will be more prone to osteoarthritis. The relationships between the different outcome measures will also be assessed. PUBLIC HEALTH RELEVANCE: ACL injuries have reached epidemic proportions and place the patient at high risk for post-traumatic arthritis. The proposed study will establish the incidence of arthritis following knee ligament surgery, and will determine if a modification in the surgical technique can reduce cartilage degeneration. It will also explore potential causes of arthritis and validate methods used to detect arthritis in the early stages of the disease. Therefore these data could impact the future care of the ACL injured patient and reduce the economic burden of post- traumatic arthritis associated with this injury.